diff --git a/docs/release-control/v6/internal/subsystems/deployment-installability.md b/docs/release-control/v6/internal/subsystems/deployment-installability.md
index 695dab5ef..5fd702dd5 100644
--- a/docs/release-control/v6/internal/subsystems/deployment-installability.md
+++ b/docs/release-control/v6/internal/subsystems/deployment-installability.md
@@ -15,6 +15,18 @@
 
 ## Purpose
 
+The shell-owned multi-tenant integration suite uses a dedicated desktop-only
+Playwright configuration selecting the seven multi-tenant scenarios. It must
+reject any non-empty E2E tier identity rather than impersonating stable or
+probation CI. Normal tier selection retains the multi-tenant quarantine.
+Diagnostic reports use invocation-specific roots under the shell runner;
+direct npm, setup and helper paths do not inherit its isolation guarantees.
+These scenarios do not establish delayed-admission, reconnect, interruption,
+installed-customer or release qualification. The executable discovery and
+tier-refusal checks in `tests/integration/scripts/managed-local-backend.test.mjs`
+protect this boundary without launching a browser.
+
+
 ### Portable installer lifecycle ownership
 
 The shared shell installer lifecycle directory (outside the least-privilege
diff --git a/tests/integration/README.md b/tests/integration/README.md
index 59a860d05..a78f54b05 100644
--- a/tests/integration/README.md
+++ b/tests/integration/README.md
@@ -289,3 +289,24 @@ Response behavior can be controlled via environment variables:
 
 - ✅ Core E2E flows pass reliably in CI
 - ✅ Update flow remains covered via API integration test + smoke UI check
+
+### Quarantined multi-tenant diagnostic
+
+From the repository root, run:
+
+```sh
+pulse-heavy-run -- bash tests/integration/scripts/run-tests.sh multi-tenant
+```
+
+This shell-owned run builds isolated images and allocates loopback ports. Its
+dedicated `playwright.multi-tenant-diagnostic.config.ts` selects only the seven
+desktop multi-tenant scenarios, including known failing scenarios. It refuses
+a non-empty `PULSE_E2E_TIER`: unset that variable explicitly for diagnostics.
+The normal stable/probation configuration and quarantine are unchanged.
+A diagnostic pass is not a stable-gate, installed-customer or release receipt.
+
+Reports remain under the invocation-specific report/result directories for
+inspection; treat browser artifacts as potentially sensitive. Direct npm,
+setup and helper invocations do not inherit the shell runner's isolation
+guarantees. The existing seven scenarios do not establish the delayed admission
+and reconnect recovery matrix.
diff --git a/tests/integration/playwright.multi-tenant-diagnostic.config.ts b/tests/integration/playwright.multi-tenant-diagnostic.config.ts
new file mode 100644
index 000000000..9248ef32e
--- /dev/null
+++ b/tests/integration/playwright.multi-tenant-diagnostic.config.ts
@@ -0,0 +1,24 @@
+import { defineConfig } from '@playwright/test';
+import base from './playwright.config';
+
+// Deliberately separate from stable/probation CI. A diagnostic result cannot
+// promote this quarantined spec or be substituted for a stable-tier verdict.
+if (process.env.PULSE_E2E_TIER?.trim()) {
+  throw new Error('Multi-tenant diagnostics cannot run as an E2E tier; unset PULSE_E2E_TIER');
+}
+
+export default defineConfig({
+  ...base,
+  testMatch: ['**/03-multi-tenant.spec.ts'],
+  outputDir: process.env.PULSE_E2E_RESULTS_DIR || 'test-results/multi-tenant-diagnostic',
+  reporter: [
+    ['list'],
+    ['html', {
+      outputFolder: process.env.PULSE_E2E_REPORT_DIR || 'playwright-report/multi-tenant-diagnostic',
+      open: 'never',
+    }],
+  ],
+  projects: base.projects!
+    .filter(project => project.name === 'chromium')
+    .map(project => ({ ...project, testIgnore: [] })),
+});
diff --git a/tests/integration/scripts/managed-local-backend.test.mjs b/tests/integration/scripts/managed-local-backend.test.mjs
index 69ad01bb5..70573e8a2 100644
--- a/tests/integration/scripts/managed-local-backend.test.mjs
+++ b/tests/integration/scripts/managed-local-backend.test.mjs
@@ -29,7 +29,7 @@ test('integration setup pins the governed Node.js major', async () => {
 
 test('buildManagedLocalBackendState uses deterministic defaults', () => {
   const state = buildManagedLocalBackendState({});
-  assert.equal(state.repoRoot.endsWith('/repos/pulse'), true);
+  assert.equal(state.repoRoot, path.resolve(integrationRoot, '../..'));
   assert.equal(state.backendVariant, 'core');
   assert.equal(state.baseURL, 'http://127.0.0.1:8765');
   assert.equal(state.metricsPort, '0');
@@ -70,7 +70,7 @@ test('buildManagedLocalBackendState supports enterprise variant with sibling rep
   );
   assert.deepEqual(state.binaryBuildArgs, ['build', '-buildvcs=false', '-o', '__OUTPUT__', './cmd/pulse-enterprise']);
   assert.ok(state.binarySourceRoots.some((root) => root.endsWith(path.join('pulse-enterprise', 'internal'))));
-  assert.ok(state.binarySourceRoots.some((root) => root.endsWith(path.join('repos', 'pulse', 'internal'))));
+  assert.ok(state.binarySourceRoots.includes(path.join(state.repoRoot, 'internal')));
 });
 
 test('buildManagedLocalBackendEnv seeds auth, bootstrap token, and billing path', () => {
@@ -169,7 +169,8 @@ test('multi-tenant release auth reuses storage state and classifies login rate l
   assert.match(multiTenantSpec, /createAuthenticatedStorageState/);
   assert.match(multiTenantSpec, /storageState:\s*async\s*\(\{\s*authStorageStatePath\s*\},\s*use\)/);
   assert.match(multiTenantSpec, /authStorageStatePath:\s*\[/);
-  assert.match(multiTenantSpec, /multi-tenant-\$\{workerInfo\.project\.name\}\.json/);
+  assert.match(multiTenantSpec, /fs\.mkdtempSync\(path\.join\(authRoot, 'multi-tenant-'\)\)/);
+  assert.match(multiTenantSpec, /finally\s*\{\s*fs\.rmSync\(authDir, \{ recursive: true, force: true \}\)/);
   assert.match(multiTenantSpec, /\{\s*scope:\s*'worker'\s*\}/);
 
   assert.match(helpers, /new URL\(response\.url\(\)\)\.pathname === "\/api\/login"/);
@@ -386,3 +387,31 @@ test('shouldBuildManagedLocalBackendFrontend skips rebuild when embedded fronten
     false,
   );
 });
+
+// Diagnostic orchestration must not impersonate a stable runtime gate.
+import { spawnSync } from 'node:child_process';
+
+function list(config, tier = '') {
+  return spawnSync(process.execPath, [
+    'node_modules/@playwright/test/cli.js', 'test',
+    '--config', config, 'tests/03-multi-tenant.spec.ts', '--list',
+  ], { cwd: integrationRoot, env: { ...process.env, PULSE_E2E_TIER: tier }, encoding: 'utf8' });
+}
+test('explicit diagnostic discovers only the seven desktop multi-tenant scenarios', () => {
+  const result = list('playwright.multi-tenant-diagnostic.config.ts');
+  assert.equal(result.status, 0, result.stdout + result.stderr);
+  assert.match(result.stdout, /Total: 7 tests in 1 file/);
+  assert.doesNotMatch(result.stdout, /mobile-chrome|mobile-safari/);
+});
+for (const tier of ['stable', 'probation']) {
+  test(`diagnostic refuses ${tier} gate identity`, () => {
+    const result = list('playwright.multi-tenant-diagnostic.config.ts', tier);
+    assert.notEqual(result.status, 0);
+    assert.match(result.stderr, /diagnostics cannot run as an E2E tier/);
+  });
+}
+test('normal stable configuration retains multi-tenant quarantine', () => {
+  const result = list('playwright.config.ts', 'stable');
+  assert.notEqual(result.status, 0);
+  assert.match(result.stdout, /Total: 0 tests/);
+});
diff --git a/tests/integration/scripts/run-tests.sh b/tests/integration/scripts/run-tests.sh
index 11d0c2ab3..5864af283 100755
--- a/tests/integration/scripts/run-tests.sh
+++ b/tests/integration/scripts/run-tests.sh
@@ -190,7 +190,7 @@ run_suite() {
             npx playwright test "tests/06-theme-visual.spec.ts" --project=chromium --reporter=list
             ;;
         multi-tenant)
-            npx playwright test "tests/03-multi-tenant.spec.ts" --project=chromium --reporter=list
+            npx playwright test --config=playwright.multi-tenant-diagnostic.config.ts --project=chromium
             ;;
         retired-trial-acquisition)
             npx playwright test "tests/07-retired-trial-acquisition.spec.ts" --project=chromium --reporter=list